Various industries, and particularly the manufacturing industry, among others, have utilized linear actuators to control the movements of automated welding guns, automated clamping fixtures, and the like. Specifically, in the automotive industry and various other industries, actuation and control of welding guns and clamping fixtures and controlled linear movement of other fixtures and devices have been accomplished using fluid actuators such as pneumatic or hydraulic actuators. While fluid actuators have functioned reasonably well for these purposes, they inherently embody various limitations. One, because of the possibility of leaks and failure of seals, etc., there is always the concern of contamination of the worksite by a leaking fluid. Second, fluid actuators necessarily require a source of pressurized fluid and thus a fluid supply system. This leads to significant maintenance and other costs. Third, limitations sometimes exist with respect to the accuracy and positioning of linear movement and the adjustability of such movement.
Various electric actuators in the prior art are built with an integral motor having a hollow rotor. Screw/nut mechanisms used in prior art actuators are typically contained within the hollow rotor. Access, therefore, to the nut component is restricted by the fact that the nut is contained within the centermost part of the actuator. Life of an actuator is determined by the life of these force transmitting components, e.g., the screw and nut. The life of the actuator may be extended by the performance of periodic maintenance, such as replenishing lubrication for the screw/nut. In the various prior art actuators, for example, those having an integral motor or hollow motor configuration as well as those having a conventional configuration, replenishing lubrication is very difficult, requiring the actuator to be partially or completely disassembled to access the components needing lubrication. In some cases, special tools are required to be purchased to access the lubrication points. In some actuators, replenishing lubrication is simply not possible.
Accordingly, there is a need in the art for an improved actuator which overcomes the deficiencies and limitations of the prior art, and in particular, an improved actuator which is designed for use in controlling the movement of, and accommodating the loads associated with, welding guns, clamping fixtures, injection molding fixtures, and various other fixtures and devices, as well as for use in numerous other industrial applications as will be recognized by those skilled in the art. A need also exists for an improved actuator with means for replenishing lubrication of the force transmitting components, which may include a lubricant passage to the internal, threaded nut.